Flowing hydrocarbon fuels and gaseous oxygen have received essentially universal application as the constituents of combustion in heat engines and various gas appliances (clothes dryers, furnaces, hot water heaters, ovens/ranges and the like). In such applications, the constituents of combustion (which are defined generically as fuel and an oxidizing agent) are combined into a flowing mixture which is ignited by the application of a mechanism which imparts electrical spark discharge energy, thermal energy from a radiant body, chemical catalytic reaction or by elevating the temperature and pressure of either or both constituents. The fuels most commonly employed are gasoline, fuel oil, methane, propane, ethane, and butane. These fuels combine with the oxidizing agent (which is most commonly gaseous oxygen found in air) to maintain an exothermic reaction once acted upon by the ignition mechanism which initiates such an exothermic reaction.
Of the various types of igniters in use, the electric spark type has gained wide acceptance. Spark plug ignition systems are used almost exclusively in internal combustion engines. Additionally, household type applicances are frequently redesigned to substitute spark igniters for systems employing continuously burning pilot lights as an energy conservation measure.
Although spark ignition of hydrocarbon fuels is a common practice, commercially available devices have a number of characteristic short-comings which vary in significance from application to application. Any electric spark effected across an air gap requires relatively high levels of power (product of voltage and current) which can present a shock hazard as well as a risk of inadvertant conflagration when employed in the vicinity of volatile fuels. Furthermore, sparking devices tend to radiate electromagnetic energy at high frequencies, and exhibit life shortenings because of metal migration between the electrodes. Maintenance of spark gap dimensions is often critical to the operation of prior art devices, necessitating relatively frequent inspection and/or servicing.
An additional shortcoming of spark igniters resides in the fact that a spark, once established between two electrodes, is a highly localized phenomenon. When a spark is employed to detonate a mixture of fuel and oxidizing agent within a combustion chamber, for example, the flame front of burning a mixture must propagate outwardly from the localized spark to envelope the entire chamber. In certain applications, this propagation time can be relatively long and result in incomplete combustion and inefficient operation of the associate device. In certain other applications, particularly when the mixture has less than the stoicometric amount of fuel, the flame front originating from the localized spark may quench, i.e., the flame front may cease to propagate and combustion may terminate prematurely.
It will become apparent from a reading of the specification that the present invention may be advantageously utilized in many different applications requiring the combustion of hydrocarbon fuels and oxidizing agents. However, the invention is especially useful when employed with household type appliances. Accordingly, the preferred embodiment of the invention will be described in that environment. Additionally, the present invention is also useful in application with internal combustion engines, and two alternative embodiments of the invention will be described in connection therewith.
The concept and characteristic operation of corona discharge devices are generally well known in other areas such as lasers, flame sensors, and smoke detectors. A widely used commercial application of corona discharge tubes is in Geiger counters.